The present invention relates to a method of and an apparatus for controlling height of a vehicle having a vehicle height adjusting device.
Conventionally motor vehicles are known that have a vehicle height adjusting device to control the height of a vehicle to zones such as high, medium and low. Motor vehicles are also known that monitor the vehicle height at a high resolution (such as in millimeter units, for example) and that independently adjust the height for each of the four wheels. Such vehicles are disclosed in Japanese Patent Laid-Open No. 139709/1987, for example.
In general, when a vehicle is stationary on a distorted road surface, a state of equilibrium is attained with some suspensions being in an extended state and other suspensions being in a contracted state. However, in vehicles having a vehicle height adjusting device as described above, and, in particular, in those vehicles that perform vehicle height adjustment at a high resolution (such as vehicles having active suspension), the suspension attempts to achieve the objective of a reference vehicle height. In the case of general vehicles that do not have a vehicle height adjusting device, the distortion of road surfaces can be absorbed by extension and contraction of the suspensions. However, in the case of vehicles having a vehicle height adjusting device, the distortion of road surfaces can only be absorbed by elastic deformation of tires of the wheels as the distortion cannot be absorbed by the extension and contraction of the suspensions. Since the spring constant of the tires is normally about one tenth of the spring constant of the suspensions, the balance between the contact loads of the wheels deteriorates and in the worst instance, the vehicle height control either does not end regardless of how much time elapses, or there occurs a status where one wheel is in a state of non-contact with the road.